Method of cleaning used steel drums of organic residues



Nov. 14, 1967 H. SMULL METHOD OF CLEANING USED STEEL DRUMS OF ORGANIC RESIDUES Filed July 17, 1962 5 Sheets-Sheet 1 INVENTOR.

HAROL D .SMUL L TW -W ATTORNEY H. SMULL 3,352,723

METHOD OF CLEANING USED STEEL DRUMS OF ORGANIC RESIDUES 5 Sheets-Sheet 2 Nov. 14, 1967 Filed July 17, 1962 A77 RNEY.

Nov. 14, 1967 SMULL 3,352,723

METHOD OF CLEANING USED STEEL DRUMS OF ORGANIC RESIDUES Filed July 17, 1962 5 Sheets-Sheet 5 #154 TERS JNVEN TOR.

HA FOL D SMUL L WJW AT ORA/E).

H. SMULL Nov. 14, 1967 METHOD OF CLEANING USED STEEL DRUMS OF ORGANIC RESIDUES Filed July 17, 1962 5 Sheets-Sheet 4 INVEN TOR.

HA ROL D .SMUL L ATTORNE).

Nov. 14, 1967 H. SMULL 3,352,723

METHOD OF CLEANING USED STEEL DRUMS OF ORGANIC RESIDUES Filed July 17, 1962 5 Sheets-Sheet 5 F 1g. /0. 40- 44 I36 36 FT 3 I j I l J )'l"")/ j J l) j 5/ 5 52 52 1 1 45 /35 45 1' 11 II II I; u t I 52 5 E1 i a ,46 J INVENTOR.

1 49.44 HAROLD SMULL. o o l i o o I l l [IL-f3: 2:131 BY L47 4a v ATTORNEY.

United States Patent 3,352,723 METHOD OF CLEANING USED STEEL DRUMS OF ORGANIC RESIDUES Harold Smull, Wynnewood, Pa., assignor to Universal Container Corporation, Louisville, Ky., a corporation of Kentucky Filed July 17, 1962, Ser. No. 211,947 3 Claims. (Cl. 148-6.15)

The present invention relates to a new and useful method of and apparatus for removing more or less solidified or generally insoluble organic residues from steel drums or steel shipping containers so as to permit the reclamation and the reprocessing or refinishing thereof for re-use.

Steel drums or shipping-containers of both the openhead type as well as the fixed-head type are used for shipping and/or storing a large variety of organic materials. When the contents have been used, or emptied or removed from the drum (in the normal course of its use), a layer of the contents remains as a residue, coating the interior surfaces of the drums.

The contents-materials and hence such contents-coatings vary widely in composition and age and hence in consistency, solidity, hardness, permeability, solubility, and resistance to chemical and mechanical removal, etc.

Thus, for instance, such residual coatings of some paints and printing inks may be removable with the aid of an organic solvent, while others may not be effectively removed by such solvent. Likewise, the residual film or coating of oils of some oil-drums may be removed :by steam or with a caustic, while drums which have been used for heavy pitch, or asphalt-base or bituminous materials would be diflicult if not impossible to clean by the same means which may be effective for ordinary oildrums. Latex and various rubber-base materials and elastomers shipped in steel drums also present problems of residue-removal.

Steel drums are also widely used for a large variety of organic plastics such as acrylic, acetal polymers and copolymers, cellulosic compounds, chlorinated polyethers, nylon and nylon compounds, polyethylenes, polypropylenes, polystyrenes and polystyrene complexes, some vinyl polymers and copolymers and other plastics and various paints, surface-coating compositions and molding compositions and the like which are compounded or formed of such plastics. The residues of these plastics are difiicult to remove from drums.

In the reclamation and refinishing of used steel drums on a commercial scale, it is uneconomical and impractical either to sort the used drums (obtained from the many diiferent users) according to the nature of their residues, or to provide a variety of processes and a corresponding assortment of different kinds of equipment to treat different kinds of residues according to their individual physical and chemical characteristics.

In addition to having to reckon with the wide variety of physical and chemical properties of the many different residues encountered in the reclamation and refinishing of steel drums on a commercial scale, it is also necessary to remove rust and oxides from both the interior and exterior surfaces of the steel drums before they can be finally refinished, and it is also necessary to remove the labeling and markings and also finish-coatings frequently provided on the exterior surfaces of the drums by various paints, enamels, lacquers and the like and also the protective coatings sometimes provided on the inside of the drums.

Where a drum reclaiming and refinishing plant can be operated for just one kind of drum-contents, as, for instance, where the plant can be confined to oil-drums of "ice - one user or of a number of like users, an economical reclamation may be achieved by subjecting the interiors of the drums to a strong caustic solution. Likewise, when a drum reclamation and refinishing plant can be confined to some other single drum-contents, some other contentsremoval method may be used which is effective for such contents alone.

Where a variety of different residues have to be removed from open-head steel drums from many different users, such drums have been heated in a furnace to burn or carbonize the organic residues therein as well as the external finish-coatings and labelings thereon, and thereafter the interior and exterior surfaces of the drums are blasted with steel shot or other steel particles to remove the last remaining residues and the rust.

The like variety of diflicult-to-remove residues in closed-head drums cannot be similarly incinerated in a furnace, because of the danger of the drums exploding or bulging, notwithstanding the fact that the bung-holes and tap-hole thereof are open-such openings being frequently insufiicient to permit the escape of the gases generated by the heating of the organic residues without the buildup of pressure which will either explode the drum or bulge it or deform it and so render it unreclaimable. Such closed-head drums have, instead, been treated with caustic alkali solution and thereafter tumbled with abrasive particles such as steel chains placed into (and later removed from) the drum through the bung-holes. Such caustic treatment is ineffective, however, for many of the organic materials encountered in the Wide variety of the so-called chemical drums, and such tumbling (or so-called chaining) will not remove residues in the corners near the crimped seams. Hence, it has also been the practice to cut off one of the heads of such closed-head drums (thereby to convert them into open-head drums) and thereafter to subject them to the aforementioned incineratingand-blasting process, and then to apply either a new or an old head to the so opened end of such drum in the manner indicated (for example) in Patent 2,943,386 issued July 5, 1960, or by crimp-seaming such head onto the drum-body-in which latter case the length and capacity of the drum is reduced.

Moreover, in incinerating or carbonizing organic residues of open-head drums in the aforementioned furnaces, temperatures of 1000 F. to 1200 F. are frequently developed because of the exothermic nature of the chemical reaction which the organic residues undergo upon such incineration; notwithstanding that the temperature of the furnace as such may be regulated to a considerably lower temperature, as, for instance, 850 F., more or less. As a result of the high temperatures, particularly the higher temperatures developed by the chemical reactions within the organic residues, there is a deterioration or destruction of the sealer-compounds commonly used in the manufacture of drums for sealing the crimped-seam between the cylindrical body and the fixed bottom of the drum and also for sealing the seam between the body of the drum and the so-called flange of the drum which provides the bung-opening. This deterioration of the sealer-compounds frequently necessitates an additional operation or operations to enhance the subsequent usefulness of the drum, or the value of the so reclaimed steel drum is reduced by reason of the fact that its subsequent reuse is limited to certain types of uses to the exclusion of others.

The aforementioned processing of open-head drums is also accompanied by the further disadvantages that the steel-shot used for removing the last remaining film or encrustation of the carbonized residue from the interior (and exterior) of the drum becomes embedded in the seam which unites the body and the bottom of the drum,

tnmbling action will dent the thinner walls of the drum so.

as to render the drums unsaleable for reuse or will so depress their resale value as to make their recovery uneconomical. Shot-blasting of such thin-gauge drums is impractical and uneconomical for the reason that such shot-blasting heats the metal to a point at which the metal softens slightly and, when so softened, such thin-gauge metal will tend to deform under the influence of the shotblasting.

Furthermore, no single process or apparatus has heretofore been found effective for a large variety of residues and conditions of open-head and closed-head drums.

The object of the present invention is a method of and apparatus for removing the organic residues from inner surfaces of open-head and closed-head steel drums and also the outer finish-coatings and labelings therefrom, which will be effective formost if not indeed all of the many different kinds of residues and outer surface-coatings which represent any significant portion of the total drum usage, so that'the reclamation and refinishing of steel drums on a commercial scale may be effected more economically by a single reclamation plant in which all such steel drums, regardless of the nature and characteristics of their organic residues will be subjected to the same method, by means of the same apparatus, for the effective removal of the interior residues and outer surface-coatings therefrom, and which will leave the so reclaimed steel drum free of rust or oxides and with both its interior and exterior surfaces in a condition suitable for receiving the new protective or finishing coatings needed to refinish the drums.

With the above objects in view, the method or process of the present invention includes moving of steel drums through highly concentrated sulfuric acid maintained at high temperature, rotating the steel drums during their passage through said acid so that the acid enters the steel drums without filling them, however, and so that the interior of the steel drum is alternately subjected to the liquid acid and to the hot vapor thereof; the exterior surface of the drum being likewise alternately subjected to the liquid and vapor phase of the hot concentrated acid, and maintaining the residence-time of the drums in said acid so that the residue on the interior of the drums will be in part carbonized and in part loosened from the interior surface of the drum and broken up by hydrogen generated by the interaction of the acid with the surface of the metal, so that the residue will thereafter be flushed out by the acid as the drum is repeatedly rotated in the acid and the acid flows into and out of the. drum and then draining all the acid out of the drum at the end of the selected residence-time and thereafter rinsing both the interior and exterior of the drum with water.

The apparatus of the present invention includes an elongated tank formed of an acid-resistant glass, preferably cellular glass having an imperforate or solid surface, said tank having inclined inlet and outlet ends, drumsupporting rails along the bottom of said tank and along inclined inlet and outlet ends thereof, having their drumsupporting surfaces above the bottom of the tank and above said inlet and outlet ends thereof, drum-guides along the sides of said tank and along the sides of said inlet and outlet ends thereof, said rails and guides being formed of a dense, solid acid-resistant glass, the distance between said side-guides being suitably in excess of the length or height of the drums, to accommodate the length of the drums with some working clearance, and also to accommodate some variation in drum-length, drum-submerging rails above the tank and generally parallel with the aforementioned drum-supporting rails for tangentially engaging the uppermost portions of the cylindrical sides of the drums to force them into the acid in the tank so as to submerge the drums in the acid in the tank to approximately one-halftmore or less) of the diameter thereof and to keep it so submerged so as to cause the acid to flow into the drums through the bung-holes and tap holes thereof as the drums are rotated during their passage through the tank, an endless-chain conveyor above the tank having drum-pushers affixed to the links thereof at suitable intervals for engaging the cylindrical walls of the drums and to move them through the tank, a drumsupply table or platform in operative alignment with the inlet-end of the tank (formed of steel plates and/ or rails) and a drain apron at the drum-discharge end of the tank formed of acid-resistant glass and having rails and guides similar to those of the tank and in alignment therewith.

The apparatus of the present invention also includes an acid-supplying, circulating, filtering and draining system, whereby the temperature, concentration and level of the acid in the tank may be maintained at the selected set-points and whereby the solids (flushed out of the drums by the acid) are in part filtered out and in part removed by the periodic draining of the acid from the bottom of the tank to make room for fresh make-up acid from the new acid supply.

The present invention further includes an air delivery, jetting and removal system for causing a layer of rapidly moving air to pass across the top of the tank, at a suitable distance above the acid level thereof, and to be withdrawn by suction means at the downstream side of the air-passage across the tank, whereby the fumes from the tank are continuously entrained in and swept away by such flat air stream across the tank and are so removed.

The apparatus of the present invention further includes a variable-speed conveyor-drive and control for adjusting the residence-time, means for sensing the temperature, concentration and level of the acid in the tank as well as the temperature and level of the acid in the filter vessel, controllers responsive to such condition-sensing means, motoroperated valves, pumps and blowers controlled by such controllers and electrical interlocking means intermediate thereof for the operative and fail-safe. maintenance of the temperature, concentration and level of the acid in the tank and for the fail-safe conditioning of the environment for the safety of operating personnel.

In the accompanying drawings, in which like reference characters indicate like parts,

FIGURE 1 represents a side elevational view of the apparatus of the present embodiment of my invention,

FIGURE 2 represents a top plan view of the same,

FIGURE 3 represents an end elevational view of the same, generally on line 33 of FIGURE 2,

FIGURE 4 represents a side elevational view of the process-vessel,

FIGURE 5 represents a top plan view of the processvessel, and including also the drain-table at the discharge end of the vessel,

FIGURE 6 represents a cross-sectional view generally on line 66 of FIGURES 4 and 5,

FIGURE 7 represents an end elevational view of the drain-table shown in FIGURES 4 and 5,

FIGURE 8 represents an end-elevational view of one of the drumushers, with the guide rails and chain-link shown in cross-section, and

FIGURE 9 represents a side elevational view of the same.

In the embodiment shown in the drawings, the processvessel or tank is designated generally by the numeral 1, has a generally horizontal main bottom-portion 2 whose length is of the order of 50 feet (more or less), a druminlet bottom-portion 3 inclined at an angle of about 19 (more or less) and of a length of the order of 5 or 6 feet (more or less), and a drum-discharge bottom-portion 4 inclined at an angle of the order of 19 (more or less) and of a length of the order of 5 or 6 feet. The processvessel 1 has side-walls 5 and 6, whose tops 7 are generally horizontal.

The process-vessel 1 is formed of an acid-resistant fused silica in the form of closed-cellular foam blocks, as indicated in FIGURES 4 and 6, having imperforate outer surfaces, which blocks are fused together or cemented together with an acid-resistant silica cement which may thereafter be fused.

The process-vessel 1, and more particularly its inclined ends, are supported on suitable structural steel supports or upon suitable concrete or masonry foundations or supports (not shown).

Guide-rails 8 and 9 (coextensive with the vessel 1) are carried by and extend inwardly from the inner surfaces of the sidewalls 5 and 6, respectively, as indicated in FIGURES 4 to 6, inclusive. The innermost portions of the guide-rails are formed of solid, dense acid-resistant glass or fused silica and are cemented and/ or fused to the inner surfaces of the side-walls of the vessel 1. The distance 10 between the inner faces of the guide-rails 8 and 9 is just suthciently in excess of the axial length or height of the steel drums to be processed, to accommodate therebetween steel drums with their axes horizontally disposed and normal to said guide nails, with sufficient allowance in the aforementioned distance 10 for the variations in such height or length of commercial steel drums, and with sufficient working clearance. The guide-rail 8 is preferably spaced inwardly a substantial distance (7" to 9") from the inner vertical surface of the side-wall 5 so as to provide a clearance-space for the electrical heaters and/or heat-exchangers 143 for maintaining the concentrated sulfuric acid in the process-vessel 1 at the required operating temperature. This inward spacing of the guide-rail 8 may be provided by mounting the rail 8 on an inwardly extending closed-cellular fused-silica shelf 11, cemented and/or fused to the inner vertical surface of the side-wall 5, as indicated in FIGURE 6.

The portions of the guide-rails 8 and 9 which are above and coextensive with the main bottom-portion 2 of the process-vessel 1, are parallel with the inner bottom surface thereof, and are spaced thereabove a distance of approximately inches (more or less). The opposite terminal portions of the guide-rails 8 and 9 which are above and generally coextensive with the inclined end-portions 3 and 4 of the process-vessel 1, incline upwardly but at an angle with respect to said inclined bottom portions 3 and 4, so that the guide-rails 8 and 9 meet the upper ends 12 and 13 of the process-vessel 1 in the manner indicated in FIGURE 4; the ends of the guide-rails 8 and 9 rising above the tops 7 of the side-Walls 5 and 6 of the processvessel 1 and also rising above (though contiguous with) the outer ends 12 and 13 of the bottom-portions 3 and 4 of the process-vessel 1.

Two or more drum-supporting rails 14 and 15, also formed of a dense acid-resistant fused-silica, are cemented and/ or fused to the inner surfaces of the bottom-portions 2, 3 and 4 of the process-vessel 1, in the manner indicated in FIGURES 4, 5 and 6. Slanted or inclined gaps 16 and 17 are provided in the portions of the supportingrails 14 and 15 which are carried by the main bottomportion 2 of the process-vessel 1, adjacent or in proximity of the drain-opening 13 extending through the side-wall 5 of the vessel, for permitting the free flow of acid from the bottom of the vessel towards and through the drainopening 18 thereof when acid is withdrawn from the vessel either to reduce the level of the acid to the desired operating level or to make room for a make-up quantity of new acid required to bring the concentration of the acid to the operating concentration or to empty the vessel entirely to any desired shut-down. By means of the gaps 16 and 17, the free flow of the acid along the bottom of the vessel 1, from the side-wall 6 to the side-wall 5, is assured, thereby providing for a flushing out of the solid sediment which accumulates on the bottom of the vessel.

The main bottom-portion 2 of the process-vessel 1 is inclined slightly from one end to the other, with its upstream end (adjacent the end-portion 3 of the vessel) being slightly lower than its downstream end (adjacent the end portion 4 of the vessel). The drain-opening 18 is provided at the lower end of the bottom-portion 2. By this means, the periodic withdrawals of portions of the acidcontent of the process-vessel 1 will tend to flush out the entire bottom-portion 2 of the process-vessel. I may, however, provide this slight incline of the main bottom-portion 2 of the vessel in the opposite direction, namely, so that the downstream end of said bottom-portion 2 is slightly lower than the upstream end thereof. When so inclining said bottom-portion, the drain-opening 18 is disposed at the lower downstream end thereof.

The portions of the drum-supporting rails 14 and 15,

which are carried by and are coextensive with the main bottom-portion 2 of the vessel, may have their upper bearing-surface disposed horizontally throughout their length, or they may have their upper bearing-surfaces inclined slightly. Thus, the upstream ends of said rails (14 and 15) may be just slightly lower than their downstream ends so as to cause a tendency of the drums to roll back- Wardly against the drum-pushers 48 thereby to prevent the drums from rolling against each other in a forward direction. I may however incline said generally horizontal supporting rails (coextensive with the bottom-portion 2) so that the downstream ends thereof are slightly lower than their upstream ends, so as to cause the drums to roll forwardly by reason of a slight gravitational effect thereon.

The guide-rails 3 and 9 and the supporting-rails 14 and 15 are substantially more resistant to abrasion or mechanical wear than the bottom-portions and side-walls of the vessel 1, and (in the embodiment shown) these rails have bearing-faces approximately 4 inches wide, and are approximately 2 inches thick, and are made up of dense acid-resistant fused-silica blocks cemented and/or fused to their supports, as mentioned above.

A drum-feed platform, designated generally by the numeral 21, is disposed at the upstream or drum-receiving end 12 of the process-vessel 1, in operative alignment with the corresponding drum-receiving ends of the supporting-rails 14 and 15, as indicated in FIGURES 1 and 2.

In the embodiment shown, the drum-feed platform or table 21 is formed of two L-shaped steel rails or angleirons 22 and 23, with one flange of each disposed in a horizontal plane and with the other flange of each disposed vertically, on the outside, at a distance from each other sufiicient to accommodate the axial dimension of the drums 24, with sufiicient working clearance, and with the upper surfaces of the horizontal flanges thereof in alignment with the upper surfaces of the receiving-ends 25 of the supporting-rails 14 and 15. The feed-rails 22 and 23 may be disposed horizontally or with a very slight forward or backward inclination. The rails 22 and 23 are supported on suitable structural steel, concrete or masonry supports (not shown). The length of the feed-rails 22 and 23 (in the embodiment shown) is of the order of 10 feet, more or less.

At the drum-discharge end of the process-vessel 1 a drain table or pan, designed generally by the numeral 27, is provided, as indicated in FIGURES 1, 2, 4, 5 and 7. In the embodiment shown, the length of the drain-table 27 is of the order of 10 feet, more or less. It is formed of closed-cellular acid-resistant fused-silica and is supported upon a structural steel, concrete or masonry support or supports (not shown), and comprises a panel-like base portion 28 formed of closed cellular acid-resistant fused-silica blocks similar to those of which the processvessel 1 is formed, and is provided with side-walls 29 and 30, which are in alignment with the guide-rails 8 and 9 (respectively) of the process-vessel 1. Drum-supporting rails 31 and 32 are mounted upon the main or base panel 28 of the drain-table 27, in alignment with the dischargeends of the supporting-rails 14 and 15 of the processvessel 1, as indicated in FIGURES l, 2, 4 and 5. The upper-bearing-surfaces of the supporting-rails 31 and 32, as well as the upper surface of the base-panel 28 of the drain-table 27 are inclined slightly in a backward direction, namely, so that their downstream or discharge ends are slightly higher than their receiving or upstream ends, whereby the acid drained from the drums while passing over the drain-table 27 will flow back into the processvessel 1, and so that the drum will not roll forwardly along the drain-table 27 by force of gravity, but only by being pushed by the drums following it and driven by the drum-pushers 26 or the drumushers 33 on the endless conveyor-chain 36.

The endless chain-conveyor, designated generally by the numeral 35, is disposed above the process-vessell and also extends above the drum-feed table or platform 21 and above the drain-table 27, as indicated generally in FIGURES 1 and 3. The conveyor includes an endless chain 36, which passes over and is interlockingly engaged by the driving sprocket-wheel 37 and also passes over the idler sprocket-wheel 38. An electric motor powered conveyor-drive 39 is operatively connected to the driving sprocket-wheel 37 through suitable chain-drive, gear-drive or other suitable driving means; the conveyor-drive 39 and its electrical control being arranged for operative processing-drive in the direction of the arrow 40, and for a jogging advancement either in the aforementioned direction or a reverse or back-up direction, with the speed of the processing-drive being preferably variable to permit the adjustment of the residence-time of the drums 24 in the process-vessel 1.

The upper or return span of the conveyor-chain 36 is supported on the horizontally disposed web of theI-beam 41, while the lower or operative span thereof is supported on the horizontal flanges of the pair of facing conveyorsupporting and drum-depressing T-shaped rails 42, as shown in FIGURE 8.

The drumushers 26 shown in FIGURES 1 and 3 as well as the differently constructed drumushers 33 and the similar but oppositely facing drum-retainers 34 shown in FIGURES 8 and 9 are secured to and carried by the conveyor-chain 36 at suitable intervals.

An oak or other suitable strip of bearing material 43 is mounted on the horizontally disposed web of the upper conveyor-supporting I-beam or rail, and the links 44 rest and slide thereon and are supported thereby along their return travel towards the sprocket-wheel 37.

The drum-pushers 33 and the similar but oppositely facing drum-retainers 34 are each formed of an L-shaped cross-bar 45 having one flange thereof secured to a link 44 and having the other or free flange thereof disposed in a right angle to therchain, as indicated in FIGURES 8 and 9. To the free flange of the cross-bar 45 a pair of bars or plates 46 are secured, and to the lower ends of the latter the pivot or trunnion bar 47 is secured, having Teflon-coated drum-pusher rollers 48 revolvably mounted and retained on its opposite projecting ends. The pair of backup rods 49 are secured to the trunnion-supporting rods or plates 46, at a suitable angle, and having abutment plates or members 50 at the free ends thereof. At a suitable distance from or at a suitable number of links away from each cross-bar 45, similar cross-bars 51 is secured to a link 44 of the chain 36, with the free flanges of such cross-bars 51 serving as stop-abutments for the back-up rods 49. This permits the opposed drum-pusher 33 and drum-retainer 34 to diverge from each other as they go around the sprocket-wheel 37 and keeps them at a predetermined spacing in relation to each other while traveling along the lower or operative span of the conveyor; the spacial and dimensional relationships of the parts being such that along the lower span of the conveyor therollers 48 of the drum-pusher 33 and the rollers 48 of the complementary or corresponding drum-retainer 34 will be spaced from each other a distance approximately equal to the diameter of the drum therebetween, plus a suitable working clearance. Teflon slide-shoes 52 are secured to each end of each of the cross-bars 45 and 51 by means of the plates 53. An I-beam or rail 54 is disposed directly above the links 44 of the lower span of the chain 36, with its web disposed horizontally and .with but a slight working clearance between the latter and the links 44, so as to prevent the links 44 and hence the drumpushers 33 and drum-retainers 34 from moving out of their prescribed positions or travel-paths while traveling along the lower or operative span of the conveyor 35 by the lifting of the chain off the rails 42.

The portion 56 of the lower conveyor-rails 42 are disposed at an angle to the drum-feed rails 22 and 23. The portions 57, 58 and 59 of the lower conveyor-rails 42 are generally parallel with the drum-supporting rails 14 and 15 of the process-vessel 1, and are spaced above the corresponding portions of such drum-supporting rails (14 and 15) a distance slightly greater than the diameter of the drums to be processed, but close enough to said drumsupporting rails 14 and 15 to depress the empty drums into the acid in the process-vessel until sufficient acid has entered the drums (through the bung-holes and/or tap holes thereof or through the open end thereof, in the case of open-head drums) to cause the drumsto sink until they rest on the drum-supporting rails 14 and 15. The portions 60 of the conveyor-rails 42, which are disposed above the drain-table 27, are parallel with the drum-supporting rails 31 and 32 thereof, as indicated in FIGURE 1.

The conveyor-rails 41 and 42 and the restrainer-rail 54 as well as the shafts of the sprocket-wheels 37 and 38 are carried by any suitable structural supports (not shown).

The drain-opening 18 of the process-vessel 1 is connected to the intake of an acid-resistant circulating-pump 61, through a conduit 62 and a shut-off valve 63; said conduit 62 being formed of sections of glass pipe and glass fittings and suitable glass connectors and having therein suitable expansion members. The circulating-pump 61 is operated by the electric-motor 64, controlled in the manner herein'below indicated.

To the delivery-port or outlet of the pump 61 a conduit is connected (having a suitable expansion section therein), and to the latter a 3-way fitting or T-fitting 65 is connected. To one of the branches of thefitting 65 a relatively small diameter conduit 66 is connected, which extends to the filter-vessel 67 and communicates with the top of the filter-chamber 68,. therein, as indicated in FIG- URES 3 and 2. To the other branch of the T-fitting 65, the, inlet of the 3-way valve 69 is connected through a suitable conduit as shown in FIGURE 3. To the outlet 71 of the valve 69 a relatively larger-dianietercd conduit or pipe 72 is connected, which also extends to and communicates with the upper portion of the filter-chamber 68 within the filter-vessel 67, as indicated in FIGURES 2 and 3. To the outlet 73 of the 3-way valve 69, a waste pipe or conduit 74 is connected, which extends to any suitable waste-collecting tank (not shown), preferably located a suitable distance from the processing-apparatus and preferably located exteriorly of the building in which such process-apparatus is housed.

An electrically powered or compressed-air powered valve-operator 75 is operativaly mounted to the 3-way valve 69 so as to set said valve automatically in any one of its several positions responsive to the process requirements as sensed and indicated by the temperature, concentration and level sensing and indicating devices hereinafter referred to. The valve-operator 75 may, by way of example, be a Bettis robot-arm controller.

The process-vessel. 67 is formed of closed-cellular acidresistant fused-silica, in the same manner as the processvessel 1, and is closed by a similarly formed lid or cover 77. A baflle 78 extends down from the cover 77 to within a short distance of the bottom 79 of the filter-vessel 67, and extends from one side-wall 80 to the other sidewall 81 thereof. Another bafiie, 82, extends upwardly from the bottom 79 of the filter-vessel 67, to a point somewhat above the bottom of the baffle 78, and spaced therefrom a suitable distance, and (like the bafiie 78) extends from the side-Wall 80 to the side-wall 81 of the filtervessel 67. The filter-chamber 68, formed between the endwall 83 of the filter-vessel 67 and the bafile i8, is packed with a suitable filter-medium, as, for instance, 1" or /2" glazed porcelain saddle-like pieces in random interlaced arrangement. The acid delivered at the top of the filterchamber 68 through the inlets 84 and/ or 85 passes downwardly through the filter-medium, and then passes beneath the lower edge of the baflie 78 and then upwardly between the baffle 78 and the baffie 82, into the acid-reservoir or chamber 86 which is formed between the baflle 78 and the end-wall 87 of the filter-vessel 67. A weir-like overflowopening 88 is provided in the end-wall 87 with a lip 89 projecting outwardly therebeneath, over which the filtered acid flows when the level of the acid in the chamber 68 rises above the weir-opening 88.

The filtered acid from the overflow 88 flows onto an inclined transfer-pan 91 (having a cover 91), the lower open end of which extends across and slightly beyond the side-wall of the process-vessel 1, as indicated in FIGURES 1, 2 and 3, thereby delivering the filtered acid into the process-vessel 1.

To an outlet 94, near the bottom of the filtered-acidchamber 86 (of the filter-vessel 67 the material-inlet of the heat-exchanger 95 is connected, through the fittings and connections 96, in the manner indicated in FIGURES l, 2 and 3. To the material-outlet of the heat-exchanger 95, a gravity-sensing and indicating device 97 is operatively connected, through the fittings and connections 98. In the embodiment shown, the gravity-sensing and indicating device 97 is an Ohmart radioactive isotope indicator, connected to a Robertshaw-Fulton recorder and controller.

A water-supply line 99 is connected to the Ohmart gravity-indicator 97 and to the heat-exchanger 95, for cooling the acid therein. Any suitable water-discharge line (not shown) is also provided for discharging the aforementioned cooling water.

From the outlet 100 of the Ohmart 97, the filtered acid is returned to the process-vessel 1 by the pipeline 101 whose discharge or outlet 102 extends over the processvessel 1, as indicated in FIGURES 1 and 3.

An acid-supply vessel 1413 is connected to the inlet of a supply-pump 104 by means of the line 195. The supplypump 104 is operated by any suitable electric motor (not shown). The outlet of the supply-pump 104 is connected to the process-vessel 1 by means of the supply line 106 whose discharge end extends over the sidewall 5 of the process-vessel 1, as indicated in FIGURE 2, so as to deliver the fresh acid into the process-vessel, from above.

A thermocouple 111 is extended downwardly from and through the shelf 11, as indicated in FIGURE 2, with its temperature-sensing portion immersed in the acid in the process-vessel 1, in a zone clear of the travel-path of the drums 25. Y

The liquid-level-sensing portion 112 of any suitable level indicating and controlling device is carried by the shelf 11 and extends downwardly therefrom into operative juxtaposition to the body of acid in the process-vessel 1. In the embodiment shown, the aforementioned level indicator and controller, is a Uehling automatic liquid level indicator and controller.

A like liquid-level indicator and controller 113 is disposed in the acid-chamber 86 (of the filter-vessel 67) as indicated in FIGURES 2 and 3.

Any suitable heating means 114, as, for instance, an electrical heater, is disposed within the acid-chamber 86 (of the filter-vessel 67) as indicated in FIGURES 2 and 3,

for maintaining the acid therein at the operating temperature of the process.

One or several flat air-jet nozzles 117 are disposed above the top of the side-wall 5 of the process-vessel 1, as indicated in FIGURES 2 and 3. The nozzle or nozzles 117 are connected by a duct or ducts 118, to the discharge 119 of an impeller type air-blower 120, driven by the electric motor 121. While in the accompanying drawings, a single nozzle 117 and one blower 120 are shown, it is to be understood that several of similar nozzles and a corresponding plurality of blowers may be provided, with the nozzles disposed side by side, to cover the entire length of the process-vessel 1.

On the opposite side of the process-vessel 1, and above the top of the side-wall 6 thereof, an air-intake 122 is disposed, which is connected to the exhaust-fan or exhaust-blower 123 through the duct 124; the exhaustblower 123 being driven by the electric motor 125 through the belt-drive 126 or any other suitable drive. The exhaustblower 123 exhausts the air (drawn in through the exhaustinlet 122) through a stack 127, to the atmosphere (either directly or through a scrubber, not shown).

Air-flow or draft switches 128 and 129 are provided in the ducts 118 and in the exhaust ducts 124 or stack 127, for monitoring the rate-of-flow of the air therein.

An air-exhaust hood 130 is provided above weir-opening 88 and above the upper open end of the transfer-pan 90. An air-duct 132, connects the exhaust-hood 130 with the duct 124 leading to the exhaust-blower 123, so that an exhaust-suction is constantly maintained above the weir-opening and transfer-pan, so as to draw off all the acid fumes thereabove which would otherwise contaminate the atmosphere.

Sweep-arms are secured to L-shaped cross-bars 13 6 afiixed to appropriately spaced links 44 of the chain 36 so as to be disposed between successive drums or drumpositions. Flexible blade-like members 137 are pendantly secured to the sweep-arms 135, and are of a length which (combined with the length of the sweep-arms 135) will bring the lower free ends or the lower free edges or edgezones of said blades 137 into sweeping contact with the inner surface of the main bottom-portion 2 of the processvessel 1. The blades 137 thus sweep the bottom of the process-vessel, including the inclined portion 4 thereof, and also sweep the upper surface of the body of acid in the process-vessel. By this means, solid particles accumulating on the bottom of the process-vessel, as well as solid particles which accumulate on the exposed upper surface of the body of acid, are continuously swept out of the process-vessel and onto the drain-table 27, and thence swept along said drain-table until swept therefrom (at the free end thereof) onto a receiving tank (not shown) disposed beneath the free end of the drain-table 27. In this manner, the solid particles which tend to accumulate on the bottom of the process-vessel or which tend to accumulate and float on top of the body of acid therein, are continuously removed, so as to keep the body of acid relatively free thereof and thereby also reduce the load upon the filter in the filter-chamber 68 of the filter-vessel 67. The sweep-blades 137 are formed of sheets of Teflon or other suitable acid-resistant and generally form-retaining resilient material of suitable thickness.

To start up the process, water (at ambient temperature of about 60 F., more or less) is placed into the process-vessel 1, from the water-supply line 141, until the amount of such water therein is just sufficient to dilute or reduce the concentration of the supply acid from the acidsupply tank 103, to the selected upper set-point of operating concentration of, for instance, 93%. Thus, by 'way of example, the fresh supply-acid in the tank 1113 may be 104.5% of sulfuric acid, which is the equivalent of 20% oleum. The amount of water placed into the processvessel 1 is readily computed (by volume) so that when the acid from the tank 103 is added thereto in an amount to raise the level of the combined liquids to the upper set- 1 1 point of operating-level of 12 or 13 inches above the upper bearing-surfaces of the drum-supporting rails 14 and 15, the aforementioned upper concentration set-point of 93% will result (or until any other selected upper set-point of concentration, up to 97% or 98% results). This addition of the fresh supply-acid to the water, in the process-vessel 1, will rise the temperature of the combined liquid to an appreciable extent, but generally not enough to reach the operating-temperature of the order of 350 F. to 450 E, which operating-temperature may be as high as 600 F. Thereupon, the series of multi-step or variableinput quartz electric heaters 143 disposed along the side of the process-vessel 1 (beneath the shelf 11 thereof) are energize until the temperature of the liquid acid within' the process-vessel 1 reaches the upper set-point value of 400 F. or such other upper set-point value as may be selected within the aforementioned ranges.

The drums 24 (to be processed) are then placed on the feed-table or rack 21, in the manner indicated in FIG- URES l and 2, and advanced until engaged by one of the drum-pushers carried by the overhead conveyor 35, which then advance the drums, in succession, into, through and out of the process-vessel 1 onto the drain-table 27, from where they are conveyed either by gravity along a downinclined set of rails or by another positive mechanical conveyor to and through a rinsing step and. subsequent phosphatizing step, referred to hereinbelow.

The speed of the conveyor 35, namely the forward speed of its drum-pushers (in the direction of the. arrow 40) is so adjusted (by the variable conveyor-drive 39) as to make the residence time of the drums within the main portion 2 of the process-vessel 1 (namely, excluding the inclined entrance-portion 3 and the inclined exit-portion 4) sufiicient for carbonizing and loosening the residuelayers within the drums. This residence-time may'vary according to the nature and thickness of the residue-layers. Thus, for instance, drums whose residue-layers are either thicker or more resistant to the acid or are thicker or are less permeable for the hydrogen-generating acid-andmetal reaction, will require a somewhat longer residencetime, while drums whose residue-layers are either thinner or of a composition more quickly carbonized by the acid or more readily penetrated for the acid-and-metal reaction, the residence-time is reduced.

So-called chemical drums, namely drums which had been used for many of the common chemical materials customarily shipped in drums and having low viscosity so that upon emptying them but a thin layer of residue remains on the interior walls of the drums, can be generally processed with a residence-time of approximately 5 minutes (more or less), while other drums having a substantially thicker residue-layer therewithin or whose residues take somewhat longer to carbonize by their inherent chemical nature, or which require a somewhat longer time for the acid to reach the metal surfaces on the interior of the drum, the residence-time may be of the order of 25 to 10 minutes, more or less.

Simultaneously with the initial heating of the water and. acid mixture in the process-vessel 1, the air-supply motor 121 and the air-exhaust motor 125 are energized so as to blow a rapidly moving stream of air across the entire (or across substantially the entire) process-vessel 1, and to exhaust said stream of air beyond the operating zone of the apparatus.

The chemical reaction between the hot concentrated acid and the residues within the drums is of an exothermic character so that the drums passing through the process-vessel impart heat to the liquid body of acid within the processvessel. The chemical reaction between the acid and the residues also forms water, which enters into the acid in the process-vessel and dilutes it. At the aforementioned operating temperature (or range of temperatures) some of the water-content of the acid and some of the acid itself vaporizes. Thus, both the free upper surface of the liquid body of acid within the process-vessel, as well as so much the process-vessel, they rotate about their axes, so that both the interior and exterior surfaces of the drums constantly move from the liquid phase to the vapor phase of the acid and vice versa.

The result of this alternate subjection of the interiorv and exterior surfaces of the drums to the liquid phase and vapor phase of the acid is in part to carbonize the residuecoatings on the interior and also the finishing coatings and labeling coatings on the exterior of the drums, and to cause theacid either in the liquid phase or in the vapor phase thereof (or in both phases thereof, alternately) to interact slightly with the metal surfaces of the drums, and so liberate a small amount of hydrogen. The hydrogen so liberated, in turn, acts to separate the coating-layers from the metal surfaces of the drums or to break the adhesion or bond between such coatings and the metal surfaces of the drums and also slightly to etch such metal surfaces.

The concentration of the acid must be maintained at a high enough level not only to withdraw the Water from the drum-residue (and from the outer surface-coatings of the drums) and thereby either to carbonize same or to render it more or less brittle or fireable, and to break the bond between such residue and the metal surfaces of the drum, but also to make the acid less reactive in relation to the metal of the drum, so that within the residence-time, the acid will react with the metal only sufiiciently to provide a minimum etching of the metal and the generation or evolution of hydrogen of an amount just sufficient to assist in the loosening of the residue-layer from the metal or to break the bond between such residue-layer and the metal.

Thus the concentration of the acid must be kept high enough at all times so that (at the operating temperature and residence-time) the reaction between the metal and the acid will not cause a significant loss of weight of metal. Any significant loss of metal by reason of the reaction of the acid therewith, would undesirably reduce the strength of the drum, when finished. Themetal-loss for one processing should be not substantially more than of the order of a half of one percent of the weight of the drum, and in.

any event not more than one percent of the weight thereof. With a SS-gallon drum weighing anywhere from 46 to 52 pounds (or sometimes slightly more), or an assumed average of 50 pounds, the weight-loss of the drum from one complete processing should be kept down to something of the order of 4 ounces (more or less), preferably lower,

The relationship between the temperature and the concentration of the acid in the process-vessel is that there should be no appreciable. surface-boiling on the upper free surface of the body of the liquid. However, some surf-aceboiling may take place at the interfaces of the acid and the heaters 143.

The vapors issuing from the upper free surface of the body of liquid will be partly water vapor and partly S0 and some S0 according to the nature of the organic ma-.

terial of the residues and the by-product of their reactions with the acid, and such of these by-products which are absorbed by the liquid body of acid.

The vapors issuing from the acid are swept and entrained or absorbed by the jetted air layer passing across the process-vessel and removed by the air-exhaust mentioned above.

This constant air-sweep across the top of the processvessel as well as the heat of vaporization requiredto produce the water and acid vapors above the liquid body of acid, tends to lower the temperature of the body of liquid acid in the process vessel. The balance between the heat supplied to the liquid body of acid by the exothermic reactions between the acid and the drum-residues acted upon, and the heat removed from the liquid body of acid by the aforementioned vaporizations and such air-sweep, may in some cases be approximately equal, namely, to maintain the temperature of the liquid body of acid at the selected operating temperature, while in most instances it will result in a steady loss of temperature or a steady lowering of the temperature of the liquid body of acid except for the additional heat supplied by the heaters 141 and 114. The heaters 143 (in the process-vessel 1) controlled by the thermostat or thermocouple 111 and complementary controller means, are arranged to supply whatever additional heat may be necessary to maintain the temperature of the body of acid at the selected operating temperature (within suitable upper and lower set-points); such heaters being automatically turned on and oif according to the heat-requirements to maintain such selected operating temperature.

The operating concentration is selected (within the aforementioned range of 85% to 98%) according to the condition of the drums or according to the requirements of the most diflicult to clean drums present in the run of drums being processed. The upper and lower set points for the maintenance of the so selected concentration are preferably as close to each other as achievable within the practical operation of the available instrumentation (in pumps and valves) and as may be dictated by economic considerations (of waste-disposal, etc.).

The liquid level of the body of acid in the processve-ssel 1 is maintained at about 12 inches above the drumsupporting rails 14 and 15, for drums Whose cylindrical bodies have an outer diameter of 22% inches (more or less), so that the level of the liquid acid within the drums (while rolling through the main portion 2 of the processvessel 1 upon the rails 14- and 15) will be slightly above the center of the drum.

The level of the body of liquid acid within the processvessel would be gradually lowered from the aforementioned 12-inch level, except for steps hereinafter referred to, because of both the evaporation or vaporization from this body of liquid, and also because of the carry-out" of liquid by the successive drums, namely, the liquid adhering to the inner and outer surfaces of the drums as they leave the exit-incline 4 or as they leave the draintable 27, and also the carry-out by reason of the incomplete drainage of the acid from the drums because of the slight undrainable pockets in closed-head drums and the slight undrainable portions in the rolling hoops of the drums.

Likewise, except for the steps hereinafter referred to, the concentration of the acid in the process-vessel would be gradually lowered, by reason of the chemical interaction between the acid and the residues and coatings on the drums and also the evaporation o-r vaporization of the liquid.

The liquid content of the process-vessel also gradually becomes contaminated with solids and also soluble material (such as salts and the like) resulting from the chemical reaction between the acid and the drum-coatings to be removed.

The aforementioned loss of liquid-level and of concentration and the aforementioned contamination are overcome by automatic additions of fresh supply-acid from the tank 103 through the supply pump 104 and corresponding or similar periodic automatic withdrawals of portions of the liquid content of the process-vessel by the circulating pump 61 and the 3-way valve 69, responsive to the condition-sensing devices hereinabove referred to.

Thu-s, the loss of liquid-level in the process-vessel (from the selected level) is automatically compensated by the delivery, into the process-vessel, of a corresponding quantity of fresh supply-acid from the tank 103 through the supply-pump 104, responsive to the liquid-level sensing by the Uehling level indicating and controlling controller 112, which automatically starts up the supply pump 104, whenever the liquid-level within the process-vessel falls to the lower set-point of the level controller.- 'When the 14 liquid level again reaches the upper set-point (of 12 inches), the Uehling level indicator and controller shuts off the supply-pump 104.

The circulating-pump 61 operates continuously (during the operation of the process) to cause a continuous flow of acid from the process-vessel 1 into the filter-vessel 67. From the filter-vessel 67 (and more particularly from the liquid-chamber 86 thereof) part of the filtered acid flows over the weir (88 and 89) down the drain-pan 90 to the process-vessel 1, while another portion of the filtered acid flows through the outlet 98 and the heat-exchanger to and through the Ohmart 97 and then from there back to the process-vessel 1, through the line 101; thereby providing a continuous filtration of the liquid contents of the process-vessel 1 and also a continuous gauging, measurement or sensing of the specific gravity and hence of the concentration of the liquid acid in the process-vessel 1.

When the concentration of the liquid acid in the processvessel (as so sensed by the Ohmart 97) drops to the lower set-point value of the selected acid concentration hereinabove referred to, the Ohmart gravity-indicator operates upon a Robertshaw-Fulton controller which, in turn, operates the Bettis robot-arm 75 of the 3-Way valve 69, so as to rotate the latter either completely or partially to divert the discharge of the circulating-pump 61 to the drain-line 74, and will maintain the 3-way valve 69 so positioned until the liquid-level in the process-vessel 1 reaches the lower set-point of the Uehling 112, at which lower setpoint the latter overcomes or disconnects, interrupts the valve-operating circuit of the aforementioned Robertshaw-Fulton controller of the Ohmart 97 and causes the 3-way valve 69 to be returned to its original re-circulating position. Simultaneously, namely, when the liquid-level in the process-vessel 1 has reached the lower set-point of the Uehling liquid-level indicator and controller 112, the latter turns on or energizes the supply pump 104 and causes fresh supply-acid to flow from the tank 103 into the process-vessel until the liquid-level in the latter rises to the upper set-point of the Uehling 112, at which upper set-point it shuts off the supply-pump 104. If upon such rise of the liquid-level to its upper set-point, the Ohmart 97 still senses an acid-concentrati-on below the upper set-point thereof, then the aforementioned cycle is repeated, namely, the 3-way valve 69 is again turned to a drain-position by the Robertshaw-Fulton regulator connected to the Ohmart 97 until the liquid-level in the process-vessel 1 drops to the lower set-point of the Uehling 112, at which point the 3-way valve 69 is re-set to its straight circulating position, and the supply-pump 104 is again activated until the liquid-level in the processvessel 1 rises to the upper set-point thereof, at which point the supply-pump 104 is again shut off; and so on until concentration of acid in the process-vessel 1 is raised to the upper set-point thereof.

The aforementioned controls are interlocked by interlocking electrical circuits (not shown).

When the steel drums leaves the process-vessel 1 (and the drain-apron 27) the surfaces of the drums have been rinsed to wash off any residual acid, such surfaces thereof are etched. Such etched surfaces are more prone to subsequent oxidization or rusting. I then immerse the drum in a phosphatizing bath of a concentrated or supersaturated aqueous solution of iron phosphate or zinc phosphate or in a mixture thereof (or such solution is sprayed onto the surfaces of the drums), thereby depositing upon the aforementioned etched surfaces of the drums the corresponding phosphate salts. The drums are then ready to have the interiors thereof spray-coated with any suitable protective coating material (according to the use to which they are to be put), and to have their exteriors spray-coated with any suitable decorative and/0r protective coating material, such as paint, lacquer, enamel, etc.

In order to remove the last residue of sulfuric acid from the drums after they leave the process-vessel 1, I may immerse the drums in a weak phosphoric acid bath or spray them with such weak acid, which also further removes any residue of oxides and further conditions the surfaces of the drums for the better reception and adherence of the aforementioned phosphatizing materials; such phosphoric acid treatment being followed by a water-rinse. The aforementioned water-rinses are preferably accomplished with cold water, and I may add thereto wetting agents and/or surfactants.

By reason of the limitedor slight interaction between the concentrated sulfuric acid in the process-vessel 1 and the inner surfaces of the steel drums and the consequent generation of hydrogen, the bond between the interfaces of the drums and the residue-layers is broken and such residue is loosened from the inner surfaces of the drums;

the acid penetrating into the interface between the drum and the residue through the residue material itself and small pores therein as well as around the residue material through gaps therein either initially present or formed by the carbonizing action of the acid.

Where the contents of the drums is very viscous as, for instance, in the case of very thick pitch or tar or similar semi-solid materials, when, consequently, only open-head drums can be used as containers, the residue layers if material left in the drum after its normal use may be considerably thicker than in the case of materials having a normal range of fluidity permitting the use of closedhead drums as shipping containers.

Where the residue layer is thus inordinately thick, and it is deemed uneconomical or undesirable to increase the residence-time of such open-head drums (in the processvcssel 1) sufliciently to obtain an adequate degradation or carbonization of the residue throughout the depth of the layer thereof, the residue-layer may be removed from the drum subsequent to the processing by the method of the present invention, by mechanical brushing or impacting the partly carbonized residue, because of the aforementioned breaking of the bond between the interface of the drum anl the residue.

Where the residue-layer is within the range of thickness commonly left behind from materials of the viscosityrange for which closed-head drums can be used as shipping containers (whether such material constitutes the residue-layer of either the open-head drum or closed-head drum) a water-rinsing of the interior of the drum by high pressure water jetted against the inner surfaces of the drum will be suflicient to dislodge and flush out all residue by means if either a stationary or a revolving nozzle or nozzles inserted into the drum, whose jet or jets will cover or traverse all portions of the interior surfaces thereof.

The residence-time of the steel drums or bodies in the aforementioned acid bath is so limited that the hydrogenproducing and metal-etching reaction between the acid and the steel at the interface between the latter and the adherent organic matter will not reduce the weight of the steel drum or body itself by an amount more than one percent (1%) and such hydrogen-producing and metaletching reaction between the acid and the steel, at the aforementioned interface, is preferably minimized to such an extent that the resultant loss of metal will be less than ore-half of one percent /2%) of the nascent steel.

By reason of the high concentration of the acid bath, its reactivity with the steel is so reduced, notwithstanding the aforementioned high temperature of the bath, that the residence-time of the steel drum or body within the bath may be extended to a length sufiicient for the acid adequately to react with the adherent organic matter (with the consequent lowering of concentration of the acid and the formation of water as the result of such reaction between the acid and the organic matter), while still keeping down the aforementioned reaction between the acid and the steel to a point at which not more than 1% or indeed substantially less than /2% of the metal is consumed by such reaction.

Thus, the aforementioned hydrogen-generation and metal-etching is generally kept to a minimum necessary for breaking the bond (or assisting in the breaking of the bond) between the organic matter and the metal or necessary for etching the metal just sufficiently to render it more receptive for the subsequent phosphatizing-deposit'and/ or protective-coatings.

Such minimizing of the hydrogen-generation and metaletching also permits the same drum to be reprocesed a number of times after a corresponding number of re-uses, without undue impairment of the physical strength of the drum.

Having described and illustrated an embodiment of my invention, I claim the following:

1. The method of reconditioning used steel drums having layers of organic matter adhering to the interior surfaces thereof, which comprises subjecting such steel drums and such adherent layers of organic matter to an aqueous sulfuric acid of a concentration of between and 98% by weight at a temperature between 350 F. and 600 F. for a length of time suflicient for the acid to react with the organic matter and to form water as a result of such reaction and to enter the interface between the steel and such organic matter adhering thereto and there to react with the steel surface just sufficiently to generate a small amount of gaseous hydrogen and to cause such hydrogen to break the bond between the surface of the steel and such organic matter and simultaneously to etch said steel surface,

2. The method of reconditioning used steel drums having layers of organic matter adhering to the interior surfaces thereof, which comprises subjecting such steel drums and such adherent layers of organic matter to an aqueous sulfuric acid of a concentration of between 80% and 98% by weight at a temperature between 350 F. and 600 F. for a length of time sufficient for the acid to react with the organicmatter and to form water as a result of such reaction and to enter the interface between the steel and such organic matter adhering thereto and there to react with the steel surface just sufficiently to generate a small amount of gaseous hydrogen and to cause such hydrogen to break the bond between the surface of the steel and such organic matter and simultaneously to etch said steel surface, thereafter impinging high-velocity jets of water against the interior of the drums to dislodgesthe organic matter whose bond with the steel has been so broken and to flush from the drums the so dislodged organic matterand the acid adhering to the interior of the drums, and thereafter subjecting said steel drums to a concentrated solution of a phosphate metal salt, at a concentration and temperature and for a length of time suflicient to cause a deposition of such phosphate salt upon the aforementioned etched surfaces of said steel drums.

3. The method of reconditioning used steel drums havsurfaces which comprises immersing such steel drums in t a bath of an aqueous sulfuric acid of a concentration of between 80% and 98% by weight at a temperature between 350 F. and 600 F. for a length of time sufiicient for the acid to react with the organic matter with a consequent dilution of the acid bath and to react with the steel at the interface between the latter and such adherent organic matter but only to an extent sufiicient to generate a small amount of gaseous hydrogen at such interface, continuously withdrawing a portion of the aforementioned acid bath and passing it through a filter and returning it to said bath, and automatically adding to said bath fresh acid at a concentration substantially above the concentration of the bath, as the concentration and volume of said bath falls, blowing a layer of high-velocity air across and in close proximity of the upper free surface of said acid bath to sweep the vapors issuing therefrom and exhausting such sweep-air and the vapors entrained therein. or absorbed thereby and p y ng added heat to Said tion and said air-sweeping.

1 7 1% bath to compensate for the heat-loss due to said vaporiza- 2,926,076 2/ 1960 Guenst 15614 2,976,201 3/1961 Perkins 15618 3,000,385 9/1961 Shay 134-57 References Cited 3,032,446 5/ 1962 Schutz et a1 13441 UNITED STATE PATENTS 3,048,503 8/1962 F0016 t a1 134-111 XR 5/193, G W t al 134 15O 3,062,223 11/1962 Marlin et a1. 13457 3 6 3,1 4,361 196 if 3 1 7/1944 Dyer 134 3 XR 4 8/ 4 Khngho 1 6 fi l y et a1 ROBERT F. B'URNETT, Primary Examiner. 2/1954 ']5 0 JACOB H. STEINBERG, ALEXANDER WYMAN, 6/1959 Hays 156-19 Exammers- 2/ 1960 Margulies 156-18 W. A. POWELL, Assistant Examiner. 

1. THE METHOD OF RECONDITIONING USED STEEL DRUMS HAVING LAYERS OF ORGANIC MATTER ADHERING TO THE INTERIOR SURFACES THEREOF, WHICH COMPRISES SUBJECTING SUCH STEEL DRUMS AND SUCH ADHERENT LAYERS OF ORGANIC MATTER TO AN AQUEOUS SULFURIC ACID OF A CONCENTRATION OF BETWEEN 80% AND 98% BY WEIGHT AT A TEMPERATURE BETWEEN 350*F. AND 600*F. FOR A LENGTH OF TIME SUFFICIENT FOR THE ACID TO REACT WITH THE ORGANIC MATTER AND TO FORM WATER AS A RESULT OF SUCH REACTION AND TO ENTER THE INTERFACE BETWEEN THE STEEL AND SUCH ORGANIC MATTER ADHERING THERETO AND THERE TO REACT WITH THE STEEL SURFACE JUST SUFFICIENTLY TO GENERATE A SMALL AMOUNT OF GASEOUS HYDROGEN AND TO CAUSE SUCH HYDROGEN TO BREAK THE BOND BETWEEN THE SURFACE OF THE STEEL AND SUCH ORGANIC MATTER AND SIMULTANEOUSLY TO ETCH SAID STEEL SURFACE. 